This application is based upon and claims the benefit of Japanese Patent Applications No. 2000-17820 filed on Jan. 21, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a method for manufacturing a (O-shaped ring sealing type) pressure detecting apparatus with a pressure detection chamber that is hermetically sealed by a resin-molded first case and a second case assembled together with an O-shaped ring interposed therebetween, and to a molding device suitably used for manufacturing the pressure detecting apparatus.
2. Description of the Related Art
As this kind of pressure detecting apparatus, for example, JP-A-7-209115 and JP-A-7-243926 propose seal diaphragm type semiconductor pressure detecting apparatuses and methods for manufacturing the same with a decreased number of parts, simplified manufacturing process, high reliability and low cost. The pressure detecting apparatuses are generally used for detecting refrigerant pressures of a vehicle air conditioner, power steering oil pressure, and the like, a detection pressure range of which is 0 to about 10 MPa.
FIG. 5A shows a cross-sectional shape of an O-shaped ring sealing type pressure detecting apparatus. A pressure detection chamber J5 is provided by assembling a molded resin case (first case) J2 holding connector pins J1 therein, and a metallic housing (second case) J4 having a seal diaphragm J3. A sensor element (integrated element) J6 fixed to a base is held in the pressure detection chamber J5 that is filled with oil J7 for transmitting pressure from the seal diaphragm J3.
At an outer periphery of the pressure detection chamber J5, an O-shaped ring J8 is fit in a groove (O-shaped ring groove) formed on an end surface of the resin case J2 in a state where it is sandwiched between a metallic pushing plate J9 of the housing J4 and the resin case J2. The O-shaped ring J8 hermetically seals the pressure detection chamber J5.
The above-described pressure detecting apparatus is generally manufactured as follows. First, the resin case is formed by injection molding with a die. The pressure detection chamber J5 holding the sensor element J6 therein is formed by assembling the resin case J2 having a recess filled with the oil J7 for the pressure detection chamber J5, and the housing J4. At that time, the O-shaped ring J8 is sandwiched and crushed between the case J2 and the housing J4 at the outer periphery of the pressure detection chamber J5, and the case J2 and the housing J4 are fixedly assembled together by caulking fixation or the like. Thus, the basic structure of the pressure detecting apparatus is manufactured.
A detecting operation of this pressure detecting apparatus is as follows. That is, pressure introduced from a pressure conduction hole J10 of the housing J4 is received by the seal diaphragm J3 and is transmitted to the oil J7. Then, the sensor element J6 detects the pressure of this oil J7, and outputs an output signal proportional to the pressure.
In the above-described detecting operation, however, if the oil J7 is leaked from the pressure detection chamber J5, the pressure cannot be transmitted appropriately. Because of this, in this kind of pressure detecting apparatus, the hermetic sealing of the pressure detection chamber J5, i.e., the sealing of the oil J7 by the O-shaped ring J8 is important. Here, FIG. 5B is an enlarged view of a portion indicated by arrow VB in FIG. 5A, and FIG. 5C is a cross-section of the O-shaped ring J8 in the radial direction thereof.
In general, the sealing property of the O-shaped ring J8 is secured by surface roughness and flatness of seal surfaces J21, J41 of the resin case J2 and the housing J4 sandwiching the O-shaped ring J8, and the compressibility of the O-shaped ring J18 compressed by the seal surfaces J21, J41. Here, the surface roughness and the flatness are set to be 12.5 S or less, and 0.05 mm or less, respectively, as values based on JIS (Japanese Industrial Standards).
The compressibility is generally in a range of 10 to 30%, which is a value represented by 100xc3x97(D1xe2x88x92D2)/D1(%). Incidentally, D1 is a diameter of the cross-section of the O-shaped ring J8 in the radial direction thereof, D2 is a diameter of the radial direction cross-section of the O-shaped ring J8 in the compressive direction. This compressibility of the O-shaped ring J8 varies due to flatness of the respective seal surfaces J21, J41. When the seal surfaces have irregularities, the compressibility varies on the circumference of the O-shaped ring J8 to have large variations. Therefore, it is important to make the respective seal surfaces flat.
The seal surface J41 of the housing J4 that is formed form metallic plate by welding can readily have satisfactory surface roughness and flatness. However, because the seal surface J21 of the resin case J2 is formed from resin by molding, the surface roughness and flatness are readily affected by its molded state. That is, in the O-shaped ring sealing type pressure detecting apparatus described above, the satisfactory surface roughness and flatness of the O-shaped ring seal surface at the resin case side cannot be attained stably.
The present invention has been made in view of the above problems. An object of the present invention is to provide a pressure detecting apparatus composed of first and second cases assembled together to form a hermetically sealed pressure detection chamber with an O-shaped ring with a sufficient sealing property. Another object of the present invention is to provide a method and a device for forming the first case from resin with a seal surface having satisfactory surface roughness and flatness.
According to the present invention, briefly, a molding die used for forming a first case has a seal correspondence surface for forming a seal surface of the first case, and a gate for injecting resin. The gate is provided at a position capable of injecting resin so that the resin flows in the molding die approximately in parallel with the seal correspondence surface. Accordingly, the resin is suppressed from hitting the seal correspondence surface of the molding die, and the seal surface formed by this molding die can have sufficient surface roughness and flatness stably.